Solar cell, manufacturing method thereof, and solar cell module

ABSTRACT

A solar cell includes: a first-conductivity-type semiconductor substrate that includes an impurity diffusion layer on one surface side, which is a light receiving surface side, the impurity diffusion layer having a second-conductivity-type impurity element diffused therein; a plurality of linear light-receiving-surface-side electrodes that are a paste electrode that has a multi-layered structure, is formed by multi-layer printing of an electrode material paste on the one surface side, and is electrically connected to the impurity diffusion layer and that extend in parallel in a specific direction in a plane direction of the semiconductor substrate; and a back-surface-side electrode that is formed on another surface side of the semiconductor substrate. In the light-receiving-surface-side electrodes, the light-receiving-surface-side electrodes get smaller in width as they get closer in a width direction of the light-receiving-surface-side electrodes to a specific reference position.

FIELD

The present invention relates to a solar cell, a manufacturing methodthereof, and a solar cell module.

BACKGROUND

A screen printing method that provides great cost advantages istypically used for forming the electrodes in bulk solar cells in whichsemiconductor crystal substrates are used. In the screen printingmethod, an electrode paste consisting of, for example, silver particles,a resin, glass frit, a solvent, and the like, is used. With the screenprinting method, the electrode paste is applied to a printing mask thatis formed with a predetermined pattern, and the electrode paste istransferred and thus printed onto a print substrate (semiconductorsubstrate) through the printing mask by moving a printing squeegee overthe printing mask. Then, the electrode paste printed on thesemiconductor substrate is fired at a predetermined temperature that isin accordance with the materials in the electrode paste, whereby anelectrode having a desired pattern is obtained.

When an electrode of a solar cell is formed, it is necessary to reducethe electrode-area percentage of the area of the semiconductor substrateon the light receiving surface side in order to capture more solar lighton the light receiving surface. Furthermore, it is necessary for formingan electrode having a low resistance to increase the cross-sectionalarea of the electrode. Thus, when an electrode of a solar cell isformed, it is necessary to form an electrode that has a small electrodewidth, a large electrode height, and a high aspect ratio.

One of the methods for obtaining an electrode having a high aspect ratioby using a screen printing method is to form a multi-layer electrode byprinting an electrode paste a plurality of times. With this method, anelectrode paste that is to be the first layer is first printed on thesubstrate and is then fired or dried at a predetermined temperature.Thereafter, an electrode paste that is to be the second layer is printedin a superposed manner on the electrode paste of the first layer and isthen fired or dried again at a predetermined temperature. Superpositionprinting is then repeated until the desired electrode height isobtained, thereby forming a multi-layer electrode.

Moreover, there is a selective emitter structure as a solar cellstructure in which an electrode portion is formed by using superpositionprinting. With this structure, in order to increase the photoelectricconversion efficiency of the solar cell, a highly doped layer(low-resistance diffusion layer, hereinafter, sometimes referred to as aterrace) is formed in a region larger than the electrode on the lightreceiving surface side of the semiconductor substrate and thus the sheetresistance is reduced, thereby increasing the conductivity. Moreover, alow doped layer (high-resistance diffusion layer) is formed in theregion other than the terrace on the light receiving surface side of thesemiconductor substrate, thereby inhibiting the recombination ofelectrons. When the selective emitter structure is used, alight-receiving-surface-side electrode is formed by printing anelectrode paste for forming the light-receiving-surface-side electrodeon the low-resistance diffusion layer in a superposed manner.

Typically, when superposition printing of an electrode paste isperformed, an alignment mark having a specific shape is used. Forexample, when an electrode paste is printed twice in a superposedmanner, the shape data and positional data on the alignment mark of thesecond layer are registered in advance as a reference image in an imageprinting apparatus. Then, at the same time as the printed material(electrode paste) of the first layer is printed on the surface of thesemiconductor substrate, an alignment mark that has the same shape asthe alignment mark described above is printed on the surface of thesemiconductor substrate.

Next, when an electrode paste of the second layer is printed, theprinting stage is first finely adjusted so that the positional data onthe alignment mark of the second layer stored in advance in the imageprinting apparatus matches the positional data on the alignment markthat has the same shape and is printed together with the electrode pasteof the first layer, and then the electrode paste of the second layer isprinted. At this point in time, the print position of the electrodepaste of the second layer to be superposed on the electrode paste of thefirst layer is aligned with reference to the positioning referenceposition that is determined in accordance with the position of thealignment mark. This operation is repeated a given number of times toform an electrode portion. By repeating this operation a given number oftimes for superposing an electrode paste, an electrode is formed.

When an electrode is formed by performing such superposition printing,if the electrode paste portion (upper-layer electrode paste portion) tobe printed next protrudes from the low-resistance diffusion layer(terrace) or the electrode paste portion (lower-layer electrode pasteportion) that is printed first (printing misalignment), thephotoelectric conversion efficiency of the solar cell is reduced. Inother words, if the light-receiving-surface-side electrode protrudesfrom the low-resistance diffusion layer (terrace) and overlaps with thehigh-resistance diffusion layer, the contact resistance between thelight-receiving-surface-side electrode and the substrate increases andthus the properties of the solar cell are reduced. As a result, thephotoelectric conversion efficiency of the solar cell is reduced.Moreover, if the upper-layer electrode paste portion protrudes from thelower-layer electrode paste portion, the light receiving area isreduced. As a result, the photoelectric conversion efficiency of thesolar cell is reduced. Thus, high superposition printing accuracy isrequired between the lower-layer electrode paste portion and theupper-layer electrode paste portion. Therefore, it is important toreduce any error that affects the high superposition printing accuracy.

In practice, however, it is not possible to eliminate all errors insuperposition printing accuracy. Thus, it is also important to addresserrors that actually occur by providing a margin such that thesuperposition itself does not fail.

There are various factors that cause an error in superposition printingaccuracy, such as a design error and a manufacturing error. However, anerror in superposition printing accuracy has a tendency to have acorrelation with a factor that is a positional relation with respect toa specific point, e.g., a tendency to have a correlation with thedistance from the printing reference point that is used when printing isperformed. Such factors include extension and a rotation error of aprinting mask because of the repeated use of the printing mask. All ofthe errors increase or decrease depending on the distance from thereference point that is used as a reference when print positioning isperformed.

The former error occurs because some of the elastic deformation of thescreen remain, i.e., becomes irreversible, when the printing mask isrepeatedly used, and the deformation rate per unit length essentiallyhas a correlation with the distance from the reference point. The lattererror is an error in the angle in the rotation direction that the wholepattern of the superposed electrode pastes may have, and this error isproportional to the angular error that occurs and to the distance fromthe reference point to each point. These errors are typically small at apoint close to the reference point and large at a point away from thereference point. Because the errors have such characteristics, there isa risk of dramatically increasing the errors depending on the location;therefore, it is important to take appropriate measures to deal withthese errors compared with other kinds of error factors.

In view of such a problem, for example, Patent Literature 1 proposes amethod of reducing extension and distortion of a printing mask. InPatent Literature 1, the percentage of the area of a screen mesh made ofa rigid material, such as a metal, in the whole area of the screen meshis set to 40% or lower in the combination printing mask having a screenmesh made of a synthetic resin and the screen mesh made of a rigidmaterial, thereby reducing extension, distortion, and the like of theprinting mask that occurs as the number of times printing is performedincreases. The purpose of this method is to eliminate the errorsthemselves.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No.2011-240623

SUMMARY Technical Problem

However, there has been a problem in that, with the method proposed inPatent Literature 1 described above, extension and distortion of theprinting mask cannot be completely prevented and the printing maskextends with repeated use.

As described above, when superposition printing is repeated by using ascreen printing method, printing errors occur because of, for example,extension and distortion of the printing mask or an angular error. Thelow-resistance diffusion layer (terrace) or the lower-layer electrodepaste portion and the upper-layer electrode paste portion are positionedby aligning them with reference to the positioning reference point.Therefore, for example, even when the printing mask extends or isdistorted, the superposition printing accuracy is still high andprinting misalignment of the upper-layer electrode paste portion issmall on the positioning reference point side, i.e., at a position nearthe positioning reference point. However, the displacement of the printposition of the upper-layer electrode paste portion gradually increasesbecause of these errors as the upper-layer electrode paste portionbecomes further away from the positioning reference point. Therefore,the risk of printing misalignment increases.

A light-receiving-surface-side electrode of a solar cell is typicallycomposed of a few bus electrodes and several grid electrodes. With theconventional technologies, the low-resistance diffusion layer (terrace)or the lower-layer electrode corresponding to the portion under the gridelectrodes is printed such that it has a uniform printing width.Accordingly, when the width of the low-resistance diffusion layer(terrace) or the lower-layer electrode paste portion is reduced,printing misalignment occurs in a portion distant from the positioningreference point and thus superposition itself fails. In such a case, theproperties of the solar cell are reduced. Providing a large margin forpreventing such printing misalignment however produces constraints.Therefore, even if there is room for thinning of the low-resistancediffusion layer (terrace) or the lower-layer electrode paste portion onthe positioning reference point side, it is still necessary to provide aredundant printing width for the low-resistance diffusion layer(terrace) or the lower-layer electrode paste portion.

The redundant width portion of the low-resistance diffusion layer, i.e.,the portion that protrudes from the light-receiving-surface-sideelectrode, becomes a factor in increasing the recombination of electronsin the semiconductor substrate. This causes a reduction in thephotoelectric conversion efficiency of the solar cell. Moreover, theredundant width portion of the lower-layer electrode paste portionbecomes a factor in increasing the electrode area of the semiconductorsubstrate on the light receiving surface side. This causes a reductionin the photoelectric conversion efficiency of the solar cell.

The present invention has been achieved in view of the above and anobject of the present invention is to provide a solar cell, amanufacturing method thereof, and a solar cell module that preventprinting misalignment of an electrode from occurring and have excellentphotoelectric conversion efficiency.

Solution to Problem

In order to solve the above problems and achieve the object, a solarcell according to an aspect of the present invention includes: afirst-conductivity-type semiconductor substrate that includes animpurity diffusion layer on one surface side, which is a light receivingsurface side, the impurity diffusion layer having asecond-conductivity-type impurity element diffused therein; a pluralityof linear light-receiving-surface-side electrodes that are a pasteelectrode that has a multi-layered structure, is formed by multi-layerprinting of an electrode material paste on the one surface side, and iselectrically connected to the impurity diffusion layer and that extendin parallel in a specific direction in a plane direction of thesemiconductor substrate; and a back-surface-side electrode that isformed on another surface side of the semiconductor substrate, whereinin the light-receiving-surface-side electrodes, thelight-receiving-surface-side electrodes get smaller in width as thelight-receiving-surface-side electrodes get closer in a width directionof the light-receiving-surface-side electrodes to a specific referenceposition.

Advantageous Effects of Invention

According to the present invention, an effect is obtained where a solarcell is obtained that prevents printing misalignment of an electrodefrom occurring and has excellent photoelectric conversion efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1-1 is a diagram illustrating the configuration of a solar cellaccording to a first embodiment of the present invention and is a topview of the solar cell when viewed from the light receiving surfaceside.

FIG. 1-2 is a diagram illustrating the configuration of the solar cellaccording to the first embodiment of the present invention and is abottom view of the solar cell when viewed from the back surface (surfaceopposite to the light receiving surface) side.

FIG. 1-3 is a diagram illustrating the configuration of the solar cellaccording to the first embodiment of the present invention and is across-sectional view of the relevant parts of the solar cell in the A-Adirection in FIG. 1-1.

FIG. 2-1 is a cross-sectional view explaining an example of amanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-2 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-3 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-4 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-5 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-6 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-7 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-8 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 2-9 is a cross-sectional view explaining an example of themanufacturing process of the solar cell according to the firstembodiment of the present invention.

FIG. 3-1 is a plan view illustrating a state where an n-type dopingpaste is printed on one surface side of a semiconductor substrate.

FIG. 3-2 is an enlarged view illustrating the relevant parts in specificregions in FIG. 3-1.

FIG. 4 is a schematic diagram illustrating a schematic configuration ofa screen printing apparatus that can perform superposition printing andthat is used for printing a paste in the first embodiment.

FIG. 5 is a diagram illustrating alignment mark portions registered inan image processing apparatus as a reference image used for positioningthe semiconductor substrate.

FIG. 6-1 is a plan view illustrating a state where a first n-typeimpurity diffusion layer is formed on one surface side of thesemiconductor substrate.

FIG. 6-2 is an enlarged view illustrating the relevant parts in thespecific regions in FIG. 6-1.

FIG. 7-1 is a plan view illustrating a state where a silver paste isprinted on one surface side of the semiconductor substrate.

FIG. 7-2 is an enlarged view illustrating the relevant parts in thespecific regions in FIG. 7-1.

FIG. 8-1 is a plan view illustrating another state where the firstn-type impurity diffusion layer is formed on one surface side of thesemiconductor substrate.

FIG. 8-2 is an enlarged view illustrating the relevant parts in specificregions in FIG. 8-1.

FIG. 8-3 is a plan view illustrating a state where a silver paste isprinted in the specific region in FIG. 8-1.

FIG. 9-1 is a plan view illustrating a state where a silver paste of thefirst layer is printed on one surface side of the semiconductorsubstrate.

FIG. 9-2 is an enlarged view illustrating the relevant parts in thespecific regions in FIG. 9-1.

FIG. 10-1 is a plan view illustrating a state where a silver paste ofthe second layer is printed on one surface side of the semiconductorsubstrate.

FIG. 10-2 is an enlarged view illustrating the relevant parts in thespecific regions in FIG. 10-1.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of a solar cell, a manufacturing method thereof,and a solar cell module according to the present invention will beexplained below in detail with reference to the drawings. The presentinvention is not limited to the following descriptions and can bemodified as appropriate without departing from the scope of the presentinvention. In the drawings explained below, for ease of understanding,the scales of respective components may be shown differently from thescales in reality. The same holds true for the relations between thedrawings. Hatching is applied even to plan views in some cases in orderto facilitate visualization of the drawings.

First Embodiment

FIG. 1-1 to FIG. 1-3 are diagrams illustrating the configuration of asolar cell according to a first embodiment, where FIG. 1-1 is a top viewof the solar cell when viewed from the light receiving surface side,FIG. 1-2 is a bottom view of the solar cell when viewed from the backsurface (surface opposite to the light receiving surface) side, and FIG.1-3 is a cross-sectional view of the relevant parts of the solar cell inthe A-A direction in FIG. 1-1.

In a solar cell 1 according to the present embodiment, on the lightreceiving surface side of a p-type polycrystalline silicon substratethat is a semiconductor substrate 2 having a first conductivity type, ann-type impurity diffusion layer 3 having a second conductivity type isformed with a thickness of about 0.2 micrometers by phosphorus diffusionso as to obtain diode characteristics, thereby forming a semiconductorsubstrate 11 that has a pn junction. An anti-reflective film 4 made froma silicon nitride film (SiN film) is formed on the n-type impuritydiffusion layer 3. The semiconductor substrate 2 having a firstconductivity type is not limited to the p-type polycrystalline siliconsubstrate and may be a p-type single crystal silicon substrate, ann-type polycrystalline silicon substrate, an n-type single crystalsilicon substrate, or other semiconductor substrates that can be used asa solar cell substrate.

Microasperities (not illustrated) are formed as a texture structure witha depth of about 10 micrometers on the surface on the light receivingsurface side of the semiconductor substrate 11 (the n-type impuritydiffusion layer 3) so as to increase the light use efficiency. Themicroasperities have a structure that increases the area by which lightfrom the outside is absorbed on the light receiving surface, reduces thereflectance on the light receiving surface, and confines light. Theanti-reflective film 4 is made from an insulating film, such as asilicon nitride film (SiN film), a silicon oxide film (SiO₂ film), and atitanium oxide film (TiO₂ film).

A plurality of long and thin linear-shaped surface silver gridelectrodes 5 are provided in parallel on the light receiving surfaceside of the semiconductor substrate 11 and thick surface silver buselectrodes 6, which are in electrical communication with the surfacesilver grid electrodes 5, are provided such that they are substantiallyperpendicular to the surface silver grid electrodes 5. The surfacesilver grid electrodes 5 and the surface silver bus electrodes 6 areelectrically connected, on their bottom surface portions, to the n-typeimpurity diffusion layer 3. The surface silver grid electrodes 5 and thesurface silver bus electrodes 6 are made from a silver material. Thesurface silver grid electrodes 5 and the surface silver bus electrodes 6are formed such that they are surrounded by the anti-reflective film 4.

The surface silver grid electrodes 5 have a predetermined width and aredisposed substantially in parallel with each other at predeterminedintervals. The surface silver grid electrodes 5 collect electricitygenerated in the semiconductor substrate 11. The surface silver buselectrodes 6 have a predetermined width larger than that of the surfacesilver grid electrodes 5. For example, two to four surface silver buselectrodes 6 are disposed per solar cell. The surface silver buselectrodes 6 extract the electricity collected by the surface silvergrid electrodes 5 to the outside. In the first embodiment, the number ofthe surface silver bus electrodes 6 is four. Alight-receiving-surface-side electrode 12, which is a comb-shaped pasteelectrode (first electrode), includes the surface silver grid electrodes5 and the surface silver bus electrodes 6. Because thelight-receiving-surface-side electrode 12 blocks solar light incident onthe semiconductor substrate 11, it is desirable from the perspective ofimproving the power generation efficiency that the area of thelight-receiving-surface-side electrode 12 is reduced as much aspossible.

In the solar cell 1, a selective emitter structure is formed by formingtwo kinds of layers as the n-type impurity diffusion layer 3.Specifically, in the surface layer portion on the light receivingsurface side of the semiconductor substrate 11, a first n-type impuritydiffusion layer 3 a is formed in the lower region under thelight-receiving-surface-side electrode 12 and the region near the lowerregion. The first n-type impurity diffusion layer 3 a is ahigh-concentration impurity diffusion layer (low-resistance diffusionlayer) in which an n-type impurity element is diffused at a highconcentration (first concentration). The light-receiving-surface-sideelectrode 12 is formed on the first n-type impurity diffusion layer 3 asuch that it does not protrude from the first n-type impurity diffusionlayer 3 a. All the surface silver grid electrodes 5 are formed with thesame width on the first n-type impurity diffusion layer 3 a.

Moreover, in the surface layer portion on the light receiving surfaceside of the semiconductor substrate 11, a second n-type impuritydiffusion layer 3 b is formed in the region in which the first n-typeimpurity diffusion layer 3 a is not formed. The second n-type impuritydiffusion layer 3 b is a low-concentration impurity diffusion layer(high-resistance diffusion layer) in which an n-type impurity element isdiffused at a low concentration (second concentration), which is lowerthan the first concentration. With such a selective emitter structure,the contact resistance between the light-receiving-surface-sideelectrode 12 and the n-type impurity diffusion layer 3 can be reduced;therefore, the photoelectric conversion efficiency of the solar cell canbe improved.

Furthermore, on the whole back surface (surface opposite to the lightreceiving surface) of the semiconductor substrate 11, a back aluminumelectrode 7 made from an aluminum material is provided and a back silverelectrode 8 made from a silver material is provided as an extractionelectrode such that it extends, for example, in substantially the samedirection as the surface silver grid electrodes 5. The back aluminumelectrode 7 and the back silver electrode 8 form a back-surface-sideelectrode 13, which is a second electrode.

An alloy layer (not illustrated) formed by firing aluminum (Al) andsilicon (Si) is formed in the surface layer portion on the back surfaceside of the semiconductor substrate 11, i.e., the portion under the backaluminum electrode 7, and a p+ layer (BSF: Back Surface Field) (notillustrated) containing a high-concentration impurity by aluminumdiffusion is formed under the alloy layer. The p+ layer (BSF) is formedin order to obtain the BSF effect and it increases the electronconcentration in the p-type layer (the semiconductor substrate 2) withthe electric field on the band structure so that electrons in the p-typelayer (the semiconductor substrate 2) do not disappear.

With the solar cell 1 configured as above, when the pn junction surface(junction surface of the semiconductor substrate 2 and the n-typeimpurity diffusion layer 3) of the semiconductor substrate 11 isirradiated with solar light from the light receiving surface side of thesolar cell 1, holes and electrons are generated. Because of the electricfield of the pn junction portion, the generated electrons move towardthe n-type impurity diffusion layer 3 and the holes move toward the p+layer. Accordingly, electrons become excessive in the n-type impuritydiffusion layer 3 and holes become excessive in the p+ layer, therebygenerating photovoltaic power. This photovoltaic power is generated in adirection that forward biases the pn junction; therefore, thelight-receiving-surface-side electrode 12 connected to the n-typeimpurity diffusion layer 3 becomes a negative electrode and the backaluminum electrode 7 connected to the p+ layer becomes a positiveelectrode. As a result, an electric current flows to an external circuit(not illustrated).

With the solar cell 1 according to the first embodiment described above,in the pattern of the first n-type impurity diffusion layer 3 a, thecomb-tooth-shaped patterns corresponding to the comb-tooth-shapedsurface silver grid electrodes 5 get thinner as they get closer in the Xdirection in FIG. 1-1 to the positioning reference point. FIG. 1-1illustrates the first n-type impurity diffusion layer 3 a through theanti-reflective film 4. In FIG. 1-1, the positioning reference point isindicated by a cross mark (hereinafter, the same applies to thedrawings). In the present embodiment, the central portion within thesurface of the semiconductor substrate 11 is the positioning referencepoint. Therefore, the width of a comb-tooth-shaped pattern 3 aL of thefirst n-type impurity diffusion layer 3 a located at the left end in theX direction in FIG. 1-1 and the width of a comb-tooth-shaped pattern 3aR of the first n-type impurity diffusion layer 3 a located at the rightend in the X direction in FIG. 1-1 are the largest. The width of acomb-tooth-shaped pattern 3 aC of the first n-type impurity diffusionlayer 3 a located in the center in the X direction in FIG. 1-1 and FIG.1-3 is the smallest. Details of the positioning reference point and thepatterns of the first n-type impurity diffusion layer 3 a will bedescribed later.

Moreover, all the surface silver grid electrodes 5 are formed with thesame width. The intervals at which the adjacent surface silver gridelectrodes 5 are disposed are all the same. All the surface silver gridelectrodes 5 are formed such that they do not protrude from the firstn-type impurity diffusion layer 3 a formed under the surface silver gridelectrodes 5.

In the surface silver grid electrode 5 at the left end in the Xdirection in FIG. 1-1, an alignment mark portion 51L is printed andformed with a silver paste in a region B in the central portion in theextending direction. In the surface silver grid electrode 5 at the rightend in the X direction in FIG. 1-1, an alignment mark portion 51R isprinted and formed with a silver paste in a region D in the centralportion in the extending direction.

Hereinafter, an explanation, with reference to the drawings, will begiven of a manufacturing method of the solar cell 1 according to thepresent embodiment configured as above. FIG. 2-1 to FIG. 2-9 arecross-sectional views explaining an example of the manufacturing processof the solar cell 1 according to the first embodiment of the presentinvention.

First, a p-type single crystal silicon substrate with a thickness of,for example, a few hundred micrometers is prepared as the semiconductorsubstrate 2 and substrate cleaning is performed (FIG. 2-1). Because thep-type single crystal silicon substrate is manufactured by slicing, witha wire saw, an ingot formed by cooling and solidifying molten silicon,damage caused by the slicing remains on the surface. Thus, the p-typesingle crystal silicon substrate is immersed in acid, such ashydrofluoric acid, or a heated alkaline solution, such as aqueous sodiumhydroxide solution, to etch the surface thereof by a thickness of about15 micrometers, thereby removing the damaged region that is generatedwhen the silicon substrate is sliced and is present near the surface ofthe p-type single crystal silicon substrate. Then, the surface of thep-type single crystal silicon substrate is cleaned with hydrofluoricacid. Thereafter, the surface of the p-type single crystal siliconsubstrate is cleaned with pure water.

Subsequent to the damage removal, anisotropic etching of the p-typesingle crystal silicon substrate is performed by immersing the p-typesingle crystal silicon substrate in a mixed solution of, for example,sodium hydroxide and IPA (isopropyl alcohol). Accordingly, a texturestructure formed with microasperities (not illustrated) with a depth of,for example, about 10 micrometers is formed on the surface on the lightreceiving surface side of the p-type single crystal silicon substrate.By providing such a texture structure on the light receiving surfaceside of the p-type single crystal silicon substrate, it is possible tocause multiple reflection of light on the front surface side of thesolar cell 1 and efficiently absorb light incident on the solar cell 1into the semiconductor substrate 11. Therefore, the reflectance can beeffectively reduced and the conversion efficiency can be improved. Whenremoval of the damaged layer and formation of the texture structure areperformed by using an alkaline solution, continuous processing isperformed in some cases by adjusting the concentration of the alkalinesolution according to individual purposes. Microasperities with a depthof about 1 micrometer to 3 micrometers may be formed on the surface of ap-type polycrystalline silicon substrate by performing a dry etchingprocess, such as reactive ion etching (RIE: Reactive Ion Etching).

Next, a pn junction is formed in the semiconductor substrate 2 byperforming a diffusion process. Specifically, for example, a V groupelement, such as phosphorus (P), is diffused into the semiconductorsubstrate 2 to form the n-type impurity diffusion layer 3 with athickness of a few hundred nanometers in the semiconductor substrate 2.

First, on one surface side to be the light receiving surface side of thesemiconductor substrate 2, an n-type doping paste 21 is applied to theregion in which the light-receiving-surface-side electrode 12 is to beformed in the subsequent processes (FIG. 2-2). The n-type doping paste21 is composed of a paste that contains an organic solvent and a resincontaining a few percentage of a V group element, such as phosphorus(P), and its compound as an n-type doping material. In the presentembodiment, the n-type doping paste 21 contains phosphorus (P) as adoping material. A screen printing method is, for example, used to applythe n-type doping paste 21.

The printing mask used for screen printing is such that a metal mesh isextended with a predetermined tension and supported within the printingmask frame made from, for example, an aluminum alloy. In other words,the printing mask frame is provided on the outer peripheral edge portionof the printing mask along the outer periphery of the printing mask andholds the metal mesh. The metal mesh is covered with a photosensitiveresin film (emulsion) in the portion except for the openingscorresponding to the printed pattern. The shape of the openingscorresponds to the pattern of the first n-type impurity diffusion layer3 a, which is formed such that it includes the pattern of thelight-receiving-surface-side electrode 12 in the plane direction of thesemiconductor substrate 2.

The n-type doping paste 21 is printed in a comb shape as illustrated inFIG. 3-1 and FIG. 3-2. This comb-shaped pattern is a pattern thatincludes the pattern of the light-receiving-surface-side electrode 12 inthe plane direction of the semiconductor substrate 2. Thelight-receiving-surface-side electrode 12 includes several surfacesilver grid electrodes 5 and a few surface silver bus electrodes 6,which are formed in the subsequent processes. In other words, thiscomb-shaped pattern includes a lower region under thelight-receiving-surface-side electrode 12 and the peripheral region thatextends from the lower region. FIG. 3-1 is a plan view illustrating astate where the n-type doping paste 21 is printed on one surface side ofthe semiconductor substrate 2. FIG. 3-2 is an enlarged view illustratingthe relevant parts in a region B, a region C, and a region D in FIG.3-1. In FIG. 3-2, (a) illustrates the region B, (b) illustrates theregion C, and (c) illustrates the region D in an enlarged scale.

The n-type doping paste 21 is printed in a pattern in which thecomb-tooth-shaped portions corresponding to the surface silver gridelectrodes 5 get smaller in width as they get closer to a specificposition in the width direction (X direction in FIG. 3-1) of the surfacesilver grid electrodes 5. In the first embodiment, in the printedpattern of the n-type doping paste 21, a comb-tooth-shaped printedpattern 21C (hereinafter, sometimes referred to as a central printedpattern 21C) of the n-type doping paste located in the center in the Xdirection in FIG. 3-1 is defined as a specific position. Othercomb-tooth-shaped portions in the printed pattern of the n-type dopingpaste 21 are such that the comb-tooth-shaped printed patterns getthinner as they get closer in the X direction in FIG. 3-1 to the centralprinted pattern 21C. Therefore, the printing width of acomb-tooth-shaped printed pattern 21L (hereinafter, sometimes referredto as a left-end printed pattern 21L) of the n-type doping paste locatedat the left end in the X direction in FIG. 3-1 and a comb-tooth-shapedprinted pattern 21R (hereinafter, sometimes referred to as a right-endprinted pattern 21R) of the n-type doping paste located at the right endin the X direction are the largest. In other words, a width “a” of theleft-end printed pattern 21L and the right-end printed pattern 21R isthe largest. A width “b” of the central printed pattern 21C is thesmallest.

When the n-type doping paste 21 is printed, as illustrated in FIG. 3-1and FIG. 3-2, an alignment mark portion 22L is printed with the n-typedoping paste 21 in the region B in the central portion in the extendingdirection of the left-end printed pattern 21L. The left-end printedpattern 21L is a comb-tooth-shaped portion located at the left end amongthe comb-tooth-shaped portions formed along a pair of opposing sides ofthe semiconductor substrate 2. The alignment mark portion 22L is printedwith the n-type doping paste 21 in a specific shape, e.g., projectingfrom the left-end printed pattern 21L.

When the n-type doping paste 21 is printed, as illustrated in FIG. 3-1and FIG. 3-2, an alignment mark portion 22R is printed with the n-typedoping paste 21 in the region D in the central portion in the extendingdirection of the right-end printed pattern 21R. The right-end printedpattern 21R is a comb-tooth-shaped portion located at the right endamong the comb-tooth-shaped portions formed along a pair of opposingsides of the semiconductor substrate 2. The alignment mark portion 22Ris printed with the n-type doping paste 21 in a specific shape, e.g.,projecting from the right-end printed pattern 21R.

The alignment mark portion 22L and the alignment mark portion 22R areused for accurately superposing the electrode on the doping pasteprinted portion in the subsequent electrode printing process. After then-type doping paste 21 is printed, the semiconductor substrate 2 is putinto a drying oven and the n-type doping paste 21 is dried at, forexample, 250° C.

FIG. 4 is a schematic diagram illustrating a schematic configuration ofa screen printing apparatus that can perform superposition printing andthat is used for printing a paste in the first embodiment. In the screenprinting apparatus, a print substrate 32 (the semiconductor substrate 2)is placed on a movable printing stage 31. The printing stage 31 canfreely move in the X direction, Y direction, and θθ direction in FIG. 4.The X direction corresponds to the X direction in FIG. 3-1. The Xdirection and the Y direction are directions that are orthogonal to eachother in the plane direction of the printing stage 31. Normally, thesquare-shaped semiconductor substrate 2 is aligned such that theextending directions of two pairs of opposing sides match the Xdirection and the Y direction, respectively, and it is placed on theprinting stage 31 with the printing side facing upward. The θ directionis a rotation direction of the printing stage 31 in the plane direction.

The alignment mark portion 22L and the alignment mark portion 22R areprinted on one surface of the semiconductor substrate 2 as describedabove. In the screen printing apparatus, a stationary camera 33, whichrecognizes an alignment mark portion, is disposed over each of thealignment mark portion 22L and the alignment mark portion 22R. Thestationary cameras 33 are connected to an image processing apparatus 34.The image processing apparatus 34 stores images captured by thestationary cameras 33. As illustrated in FIG. 5, in the image processingapparatus 34, shape data and positional data on an alignment markportion 35L and an alignment mark portion 35R are registered in advanceas a reference image 35 used for positioning the semiconductor substrate2. The alignment mark portion 35L corresponds to the alignment markportion 51L, which is printed simultaneously with an electrode pastethat will be described later, and the alignment mark portion 35Rcorresponds to the alignment mark portion 51R, which is printedsimultaneously with an electrode paste that will be described later.FIG. 5 is a diagram illustrating the alignment mark portions registeredin the image processing apparatus 34 as the reference image 35 used forpositioning the semiconductor substrate 2.

Next, the semiconductor substrate 2 to which the n-type doping paste 21is applied is put into a thermal diffusion furnace and a thermaldiffusion process of thermally diffusing a dopant (phosphorus) isperformed. In this process, phosphorus is thermally diffused at a hightemperature in phosphorus oxychloride (POCl₃) gas by using a vapor-phasediffusion method. The n-type doping paste 21 contains a dopant(phosphorus) at a concentration higher than that of phosphorusoxychloride (POCl₃) gas. Therefore, on one surface side of thesemiconductor substrate 2, more dopant (phosphorus) is thermallydiffused into the portion under the region in which the n-type dopingpaste 21 is printed than in other regions. Accordingly, a dopant(phosphorus) is thermally diffused at a high concentration (firstconcentration) from the n-type doping paste 21 into the region under theprinted region of the n-type doping paste 21 on one surface side of thesemiconductor substrate 2, thereby forming the first n-type impuritydiffusion layer 3 a (FIG. 2-3). In other words, the pattern of the firstn-type impurity diffusion layer 3 a on one surface side of thesemiconductor substrate 2 corresponds to the printed pattern of then-type doping paste 21 on one surface side of the semiconductorsubstrate 2.

With this thermal diffusion process, in the region excluding the printedregion of the n-type doping paste 21 on the surface of the semiconductorsubstrate 2, i.e., the exposed region of the semiconductor substrate 2,a dopant (phosphorus) is thermally diffused at a concentration (secondconcentration) lower than that in the first n-type impurity diffusionlayer 3 a, thereby forming the second n-type impurity diffusion layer 3b (FIG. 2-3). Accordingly, a selective emitter structure composed of thefirst n-type impurity diffusion layer 3 a and the second n-type impuritydiffusion layer 3 b is obtained as the n-type impurity diffusion layer 3on the light receiving surface side of the semiconductor substrate 2.The sheet resistance of the semiconductor substrate 11 on the lightreceiving surface side is, for example, such that the sheet resistanceof the first n-type impurity diffusion layer 3 a to be the region underthe light-receiving-surface-side electrode 12 is 20Ω/□ to 40Ω/□ and thesheet resistance of the second n-type impurity diffusion layer 3 b to bethe light receiving surface is 80Ω/□ to 120Ω/□.

FIG. 6-1 is a plan view illustrating a state where the first n-typeimpurity diffusion layer 3 a is formed on one surface side of thesemiconductor substrate 2. FIG. 6-2 is an enlarged view illustrating therelevant parts in the region B, the region C, and the region D in FIG.6-1. In FIG. 6-2, (a) illustrates the region B, (b) illustrates theregion C, and (c) illustrates the region D in an enlarged scale. Asillustrated in FIG. 6-1, the pattern of the first n-type impuritydiffusion layer 3 a on one surface side of the semiconductor substrate 2corresponds to the printed pattern (comb-shaped) of the n-type dopingpaste 21 on one surface side of the semiconductor substrate 2.

Therefore, as illustrated in FIG. 6-2, the comb-tooth-shaped pattern 3aC (hereinafter, sometimes referred to as the central first n-typeimpurity diffusion layer 3 aC) of the first n-type impurity diffusionlayer 3 a located in the center in the X direction in FIG. 6-1 is formedin the shape of the central printed pattern 21C. The comb-tooth-shapedpattern 3 aL (hereinafter, sometimes referred to as the left-end firstn-type impurity diffusion layer 3 aL) of the first n-type impuritydiffusion layer 3 a located at the left end in the X direction in FIG.6-1 is formed in the shape of the left-end printed pattern 21L. Thecomb-tooth-shaped pattern 3 aR (hereinafter, sometimes referred to asthe right-end first n-type impurity diffusion layer 3 aR) of the firstn-type impurity diffusion layer 3 a located at the right end in the Xdirection in FIG. 6-1 is formed in the shape of the right-end printedpattern 21R.

Other comb-tooth-shaped portions in the pattern of the first n-typeimpurity diffusion layer 3 a are such that the comb-tooth-shapedpatterns get thinner as they get closer in the X direction in FIG. 6-1to the central first n-type impurity diffusion layer 3 aC. Therefore,the width “a” of the left-end first n-type impurity diffusion layer 3 aLand the right-end first n-type impurity diffusion layer 3 aR is thelargest. The width “b” of the central first n-type impurity diffusionlayer 3 aC is the smallest. In the present embodiment, for example, thewidth “a” of the left-end first n-type impurity diffusion layer 3 aL andthe right-end first n-type impurity diffusion layer 3 aR is 200micrometers and the width “b” of the central first n-type impuritydiffusion layer 3 aC closest to the positioning reference point is 120micrometers.

An alignment mark portion 41L of the first n-type impurity diffusionlayer 3 a is formed in the shape of the alignment mark portion 22Lprinted with the n-type doping paste 21. An alignment mark portion 41Rof the first n-type impurity diffusion layer 3 a is formed in the shapeof the alignment mark portion 22R printed with the n-type doping paste21.

The concentration of phosphorus to be diffused in this case can becontrolled in accordance with the concentration of the dopant(phosphorus) in the n-type doping paste 21, the concentration andatmosphere temperature of phosphorus oxychloride (POCl₃) gas, and theheating time. A glassy (PSG: Phospho-Silicate Glass) layer (notillustrated) deposited on the surface during the diffusion process isformed on the surface of the semiconductor substrate 2 immediately afterthe thermal diffusion process.

Next, pn isolation is performed (not illustrated). Because the secondn-type impurity diffusion layer 3 b is formed uniformly on the surfacesof the semiconductor substrate 2, one surface side and the other surfaceside of the semiconductor substrate 2 are electrically connected to eachother. Thus, when the back aluminum electrode 7 (p-type electrode) andthe light-receiving-surface-side electrode 12 (n-type electrode) areformed in this state, the back aluminum electrode 7 (p-type electrode)and the light-receiving-surface-side electrode 12 (n-type electrode) areelectrically connected. In order to interrupt this electricalconnection, pn isolation is performed by removing the second n-typeimpurity diffusion layer 3 b formed in the end surface region of thesemiconductor substrate 2, e.g., by dry etching or using a laser.

Next, the semiconductor substrate 2 is immersed, for example, in ahydrofluoric acid solution and then undergoes a washing process so as toremove the glassy material formed on the surface of the semiconductorsubstrate 2 during the thermal diffusion process and the glassy material(a mass after a phosphorus compound is dissolved) that is a residue ofthe n-type doping paste 21 (FIG. 2-4). Accordingly, the semiconductorsubstrate 11 is obtained in which a pn junction is formed by thesemiconductor substrate 2, which is the first-conductivity-type layerand is made from p-type silicon, and the n-type impurity diffusion layer3, which is the second-conductivity-type layer and is formed on thelight receiving surface side of the semiconductor substrate 2.

Next, a silicon nitride (SiN) film is, for example, formed with auniform thickness (e.g., 60 nanometers to 80 nanometers) as theanti-reflective film 4 on the light receiving surface side (the n-typeimpurity diffusion layer 3 side) of the semiconductor substrate 11 (FIG.2-5). The anti-reflective film 4 is formed by using a plasma CVD methodand using a mixed gas of silane (SiH₄) gas and ammonia (NH₃) gas as araw material.

Electrodes are then formed by screen printing. First, theback-surface-side electrode 13 (before firing) is formed by screenprinting. Specifically, a back silver electrode, which is an externalextraction electrode that ensures conduction to an external source, isformed by printing a silver paste 8 a, which is an electrode materialpaste containing silver particles, on the back surface of thesemiconductor substrate 11 in the desired back silver electrode patternand drying the silver paste 8 a (FIG. 2-6).

Next, an aluminum paste 7 a, which is an electrode material pastecontaining aluminum particles, is applied to and printed on the backsurface side of the semiconductor substrate 11 excluding the patternportion of the back silver electrode 8 in the shape of the back aluminumelectrode 7, and then the aluminum paste 7 a is dried (FIG. 2-7).

Next, the light-receiving-surface-side electrode 12 (before firing) isformed by screen printing. Specifically, a silver paste 12 a, which isan electrode material paste containing glass frit and silver particles,is applied to the anti-reflective film 4 on the light receiving surfaceof the semiconductor substrate 11 by screen printing in the shape of thesurface silver grid electrodes 5 and the surface silver bus electrodes6, and then the silver paste is dried (FIG. 2-8). In FIG. 2-8, only asilver paste 5 a portion for forming the surface silver grid electrodes5 of the silver paste 12 a is illustrated.

The silver paste for forming the light-receiving-surface-side electrode12 is printed such that it is superposed on the doping paste printedportion on one surface side of the semiconductor substrate 11, i.e., thefirst n-type impurity diffusion layer 3 a formed on one surface side ofthe semiconductor substrate 11. FIG. 7-1 is a plan view illustrating astate where the silver paste 12 a is printed on one surface side of thesemiconductor substrate 11. FIG. 7-2 is an enlarged view illustratingthe relevant parts in the region B, the region C, and the region D inFIG. 7-1. In FIG. 7-2, (a) illustrates the region B, (b) illustrates theregion C, and (c) illustrates the region D in an enlarged scale. Theprinted pattern of the silver paste is printed in a superposed manner onthe first n-type impurity diffusion layer 3 a in the following manner.

First, the printing stage 31 on which the semiconductor substrate 11 isplaced is finely adjusted such that the position (data) of the alignmentmark portion 35L registered in advance in the image processing apparatus34 as the reference image 35 and the position (data) of the alignmentmark portion 41L of the first n-type impurity diffusion layer 3 a matchwithin a predetermined error range. Moreover, the printing stage 31 onwhich the semiconductor substrate 11 is placed is finely adjusted suchthat the position (data) of the alignment mark portion 35R registered inadvance in the image processing apparatus 34 as the reference image 35and the position (data) of the alignment mark portion 41R of the firstn-type impurity diffusion layer 3 a match within a predetermined errorrange.

Then, as illustrated in FIG. 7-1 and FIG. 7-2, the silver paste 12 a isprinted on the first n-type impurity diffusion layer 3 a. Therefore, asillustrated in FIG. 7-2, a comb-tooth-shaped printed pattern 5 aC(hereinafter, sometimes referred to as a central printed pattern 5 aC)of the surface silver grid electrode located in the center in the Xdirection in FIG. 7-1 is printed on the central first n-type impuritydiffusion layer 3 aC. A comb-tooth-shaped printed pattern 5 aL(hereinafter, sometimes referred to as a left-end printed pattern 5 aL)of the surface silver grid electrode located at the left end in the Xdirection in FIG. 7-1 is printed on the left-end first n-type impuritydiffusion layer 3 aL. A comb-tooth-shaped printed pattern 5 aR(hereinafter, sometimes referred to as a right-end printed pattern 5 aR)of the surface silver grid electrode located at the right end in the Xdirection in FIG. 7-1 is printed on the right-end first n-type impuritydiffusion layer 3 aR.

Other comb-tooth-shaped portions in the printed pattern of the silverpaste 5 a for forming the surface silver grid electrodes 5 are alsoprinted on the comb-shaped first n-type impurity diffusion layer 3 a ina similar manner. Moreover, the silver paste 12 a for forming thesurface silver bus electrodes 6 is also printed on the correspondingfirst n-type impurity diffusion layer 3 a. The silver paste for thesurface silver grid electrodes is printed such that it has a uniformprinting width “c”. In the first embodiment, the printing width “c” ofthe silver paste for the surface silver grid electrodes is, for example,100 micrometers. The silver paste for the surface silver grid electrodes5 is printed such that the printing intervals between the surface silvergrid electrodes 5 are all the same.

When the silver paste 12 a is printed, as illustrated in FIG. 7-1 andFIG. 7-2, the alignment mark portion 51L is printed with the silverpaste 12 a in the region B in the central portion in the extendingdirection of the left-end printed pattern 5 aL. The left-end printedpattern 5 aL is a comb-tooth-shaped portion located at the left endamong the comb-tooth-shaped portions formed along a pair of opposingsides of the semiconductor substrate 2. The alignment mark portion 51Lhas a specific shape, e.g., projecting from the left-end printed pattern5 aL and has a shape corresponding to the alignment mark portion 41L ofthe first n-type impurity diffusion layer 3 a.

When the silver paste 12 a is printed, as illustrated in FIG. 7-1 andFIG. 7-2, the alignment mark portion 51R is printed with the silverpaste 12 a in the region D in the central portion in the extendingdirection of the right-end printed pattern 5 aR. The right-end printedpattern 5 aR is a comb-tooth-shaped portion located at the right endamong the comb-tooth-shaped portions formed along a pair of opposingsides of the semiconductor substrate 2. The alignment mark portion 51Rhas a specific shape, e.g., projecting from the right-end printedpattern 5 aR and has a shape corresponding to the alignment mark portion41R of the first n-type impurity diffusion layer 3 a.

The silver paste 12 a is printed in a state where the position (printposition of the silver paste 12 a) of the printing stage for printingthe silver paste 12 a is adjusted such that the position of thealignment mark portion 41L of the first n-type impurity diffusion layer3 a matches the position of the alignment mark portion 51L correspondingto the alignment mark portion 35L and the position of the alignment markportion 41R of the first n-type impurity diffusion layer 3 a matches theposition of the alignment mark portion 51R corresponding to thealignment mark portion 35R.

At this point in time, the point at which the silver paste 12 a and thefirst n-type impurity diffusion layer 3 a are superposed on each otherwith the highest accuracy is referred to as the positioning referencepoint. In the present embodiment, an alignment mark is provided in eachof the region B in the central portion in the extending direction of theleft-end printed pattern 5 aL and the region D in the central portion inthe extending direction of the right-end printed pattern 5 aR;therefore, the central portion within the surface of the semiconductorsubstrate 11 is the positioning reference point. In FIG. 7-1, thepositioning reference point is indicated by a cross mark.

The printing mask used for printing the silver paste 12 a is a printingmask that has a plurality of opening patterns disposed in parallel atequal intervals. The opening patterns have the same width that issmaller than the width of the first n-type impurity diffusion layer 3 athat is closest to the positioning reference point in the widthdirection of the first n-type impurity diffusion layer 3 a. The firstn-type impurity diffusion layer 3 a that is closest to the positioningreference point in the width direction of the first n-type impuritydiffusion layer 3 a and the opening pattern corresponding to theposition of that first n-type impurity diffusion layer 3 a are alignedwith the highest accuracy.

The first n-type impurity diffusion layer 3 a portion and the printposition of the silver paste 12 a are aligned with reference to thepositioning reference point (they are superposed with high accuracy nearthe positioning reference point). Therefore, even when extension,distortion, or the like occurs in the printing mask used for printingthe silver paste 12 a, printing misalignment does not occur near thepositioning reference point because the printing accuracy is high nearthe positioning reference point.

The print position of the silver paste 12 a is gradually displaced as itbecomes further away from the positioning reference point; therefore,printing misalignment occurs. Thus, the first n-type impurity diffusionlayer 3 a that is located away from the positioning reference point hasa certain width such that the silver paste 12 a does not protrude fromthe first n-type impurity diffusion layer 3 a during the printingprocess of the silver paste 12 a. In other words, the comb-tooth-shapedportions in the pattern of the first n-type impurity diffusion layer 3 aare such that the comb-tooth-shaped patterns get thicker as they getfurther away from the positioning reference point.

Because the printing accuracy of the silver paste 12 a is high at aposition near the positioning reference point, the width of the firstn-type impurity diffusion layer 3 a is made smaller near the positioningreference point. Accordingly, the area occupied by the first n-typeimpurity diffusion layer 3 a (high-concentration impurity diffusionlayer) in the n-type impurity diffusion layer 3 is reduced. Therefore,the recombination of electrons in the semiconductor substrate 11 can bereduced and thus the electrical properties of the solar cell can beimproved. In the present embodiment, as described above, for example,the width “a” of the left-end first n-type impurity diffusion layer 3 aLand the right-end first n-type impurity diffusion layer 3 aR, which arefurthest from the positioning reference point in the width direction ofthe surface silver grid electrodes 5, is 200 micrometers and the width“b” of the central first n-type impurity diffusion layer 3 aC closest tothe positioning reference point is 120 micrometers.

As described above, the pattern of the silver paste 12 a is printed suchthat it is superposed on the n-type impurity diffusion layer 3. Evenwhen the printing mask used for printing the silver paste 12 a has aprinting misalignment amount “d” of, for example, 50 micrometers becauseof its extension, distortion, or the like, the left-end printed pattern5 aL and the right-end printed pattern 5 aR having a width of 100micrometers are printed without protruding from the left-end firstn-type impurity diffusion layer 3 aL and the right-end first n-typeimpurity diffusion layer 3 aR, which are furthest from the positioningreference point and have a width of 200 micrometers.

In such a manner, the area of the first n-type impurity diffusion layer3 a (high-concentration impurity diffusion layer) near the positioningreference point can be reduced without causing printing misalignment ofeven the surface silver grid electrode 5 located away from thepositioning reference point in the width direction of the surface silvergrid electrodes 5 from the first n-type impurity diffusion layer 3 a.Therefore, in addition to the improvement of the properties due to theselective emitter structure, the properties can be further improved andthe cost of forming the first n-type impurity diffusion layer 3 a(high-concentration impurity diffusion layer) can be reduced.

In other words, by preventing printing misalignment of the surfacesilver grid electrodes 5 from the first n-type impurity diffusion layer3 a from occurring, an increase is prevented in the contact resistancebetween the light-receiving-surface-side electrode 12 and thesemiconductor substrate 11 (the n-type impurity diffusion layer 3) dueto the light-receiving-surface-side electrode 12 protruding from thefirst n-type impurity diffusion layer 3 a and overlapping with thesecond n-type impurity diffusion layer 3 b and thus the properties ofthe solar cell are prevented from being reduced. Therefore, thephotoelectric conversion efficiency of the solar cell 1 can be improved.Printing misalignment of the surface silver grid electrodes 5 from thefirst n-type impurity diffusion layer 3 a causes an increase in the areaof the unnecessary first n-type impurity diffusion layer 3 a(high-concentration impurity diffusion layer) that does not contributeto the improvement of the conductivity with the surface silver gridelectrodes 5 and that causes an increase in the recombination ofelectrons in the semiconductor substrate 11.

Moreover, by reducing the area of the first n-type impurity diffusionlayer 3 a (high-concentration impurity diffusion layer) near thepositioning reference point, the area occupied by the first n-typeimpurity diffusion layer 3 a (high-concentration impurity diffusionlayer) in the n-type impurity diffusion layer 3 is reduced. Therefore,the recombination of electrons in the semiconductor substrate 11 can bereduced and thus the electrical properties of the solar cell can beimproved.

Thereafter, by firing the electrode pastes on the front and backsurfaces of the semiconductor substrate 11 at the same time, on thefront side of the semiconductor substrate 11, the silver material comesinto contact with silicon and is re-solidified while the anti-reflectivefilm 4 is melting by the glass material contained in the silver paste.Accordingly, the surface silver grid electrodes 5 and the surface silverbus electrodes 6, which form the light-receiving-surface-side electrode12, are obtained and thus the light-receiving-surface-side electrode 12and the n-type impurity diffusion layer 3 are electrically connected toeach other (FIG. 2-9). Such a process is referred to as a fire-throughmethod. Therefore, the n-type impurity diffusion layer 3 can have anexcellent resistive junction with the light-receiving-surface-sideelectrode 12. Firing is performed, for example, at 750° C. to 800° C. orhigher by using an infrared heating furnace.

On the back surface side of the semiconductor substrate 11, the aluminumpaste 7 a and the silver paste 8 a are fired; therefore, the backaluminum electrode 7 and the back silver electrode 8 are formed, andfurthermore, the connection portions of the back aluminum electrode 7and the back silver electrode 8 are formed as an alloy portion.Concurrently with this, the aluminum paste 7 a is also alloyed withsilicon on the back surface of the semiconductor substrate 11 and,during the re-solidification process thereof, a BSF layer (notillustrated) containing aluminum as a dopant is formed immediately underthe back aluminum electrode 7. Accordingly, the n-type impuritydiffusion layer 3 formed on the back surface side of the semiconductorsubstrate 11 is inverted to a p-type layer; therefore, the pn junctionon the back surface of the semiconductor substrate 11 can be nullified.

The method for determining the positioning reference point is notlimited to the example described above. For example, as illustrated inFIG. 8-1 and FIG. 8-2, an alignment mark portion may be provided in thefirst n-type impurity diffusion layer 3 a that is on one end side in thewidth direction (X direction in FIG. 8-1) of the comb-shaped firstn-type impurity diffusion layer 3 a and in the first n-type impuritydiffusion layer 3 a other than that on the end portion side in the widthdirection (X direction in FIG. 8-1) of the comb-shaped first n-typeimpurity diffusion layer 3 a. In the printed pattern of the silver paste5 a for forming the surface silver grid electrodes 5, alignment markportions are provided at the positions corresponding to the alignmentmark portions of the first n-type impurity diffusion layer 3 a.

FIG. 8-1 is a plan view illustrating another state where the firstn-type impurity diffusion layer 3 a is formed on one surface side of thesemiconductor substrate 2. FIG. 8-2 is an enlarged view illustrating therelevant parts in a region E, a region F, a region G, and a region H inFIG. 8-1. In FIG. 8-2, (a) illustrates the region E, (b) illustrates theregion F, (c) illustrates the region G, and (d) illustrates the region Hin an enlarged scale. FIG. 8-3 is a plan view illustrating a state wherethe silver paste 5 a is printed in the region H in FIG. 8-1. Asillustrated in FIG. 8-1, the pattern of the first n-type impuritydiffusion layer 3 a on one surface side of the semiconductor substrate 2corresponds to the printed pattern (comb-shaped) of the n-type dopingpaste 21 on one surface side of the semiconductor substrate 2.

As illustrated in FIG. 8-1 and FIG. 8-2, an alignment mark portion 42Laand an alignment mark portion 42Lb of the first n-type impuritydiffusion layer 3 a are formed in the left-end first n-type impuritydiffusion layer 3 aL. An alignment mark portion 42L3 of the first n-typeimpurity diffusion layer 3 a is formed in a comb-tooth-shaped firstn-type impurity diffusion layer 3 aL3, which is located third from theleft in the width direction (X direction in FIG. 8-1) of the comb-shapedfirst n-type impurity diffusion layer 3 a. In this case, the lower leftportion of the semiconductor substrate 2 in FIG. 8-1 is the positioningreference point.

Other comb-tooth-shaped portions in the pattern of the first n-typeimpurity diffusion layer 3 a are such that the comb-tooth-shapedpatterns get thinner as they get closer in the X direction in FIG. 8-1to the left-end first n-type impurity diffusion layer 3 aL. Therefore, awidth “f” of the right-end first n-type impurity diffusion layer 3 aR isthe largest. A width “e” of the left-end first n-type impurity diffusionlayer 3 aL is the smallest.

In this case, for example, the width “e” of the left-end first n-typeimpurity diffusion layer 3 aL closest to the positioning reference pointin the width direction (X direction in FIG. 8-1) of the comb-shapedfirst n-type impurity diffusion layer 3 a is 120 micrometers, and thewidth “f” of the right-end first n-type impurity diffusion layer 3 aRfurthest from the positioning reference point is 200 micrometers. Evenwhen the printing mask used for printing the silver paste 12 a has aprinting misalignment amount “g” of, for example, 50 micrometers becauseof its extension, distortion, or the like, the right-end printed pattern5 aR having a width of 100 micrometers is printed without protrudingfrom the right-end first n-type impurity diffusion layer 3 aR, which isfurthest from the positioning reference point and has a width of 200micrometers.

As described above, in the first embodiment, the first n-type impuritydiffusion layer 3 a that is located away from the positioning referencepoint in the width direction of the surface silver grid electrodes 5 hasa width with a certain margin such that the silver paste 12 a does notprotrude from the first n-type impurity diffusion layer 3 a during theprinting process of the silver paste 12 a. In other words, thecomb-tooth-shaped portions in the pattern of the first n-type impuritydiffusion layer 3 a are such that the comb-tooth-shaped patterns getthicker as they get further away from the positioning reference point.Because the printing accuracy of the silver paste 12 a is high at aposition near the positioning reference point, the width of the firstn-type impurity diffusion layer 3 a is made smaller near the positioningreference point. Accordingly, the area of the first n-type impuritydiffusion layer 3 a (high-concentration impurity diffusion layer) nearthe positioning reference point can be reduced without causing printingmisalignment of the surface silver grid electrode 5 located away fromthe positioning reference point in the width direction of the surfacesilver grid electrodes 5. Therefore, in addition to the improvement ofthe properties due to the selective emitter structure, the propertiescan be further improved and the cost of forming the first n-typeimpurity diffusion layer 3 a (high-concentration impurity diffusionlayer) can be reduced.

Therefore, according to the first embodiment, a solar cell is obtainedin which a reduction in the photoelectric conversion efficiency due tothe printing misalignment of the light-receiving-surface-side electrodeis prevented and that has excellent photoelectric conversion efficiency.

Second Embodiment

The above first embodiment has described the case where an electrodepaste is printed on the n-type impurity diffusion layer(high-concentration impurity diffusion layer) portion in a selectiveemitter structure to form a light-receiving-surface-side electrodewithout causing printing misalignment. The second embodiment willdescribe a case where an electrode having a multilayered structure isformed by printing an electrode paste a plurality of times in asuperposed manner.

In this case, during the printing process of a silver paste for formingthe light-receiving-surface-side electrode, the silver paste is printeda plurality of times in a superposed manner. In the present embodiment,an explanation will be given of a case where the silver paste is printedtwice during the printing process of the silver paste for forming thelight-receiving-surface-side electrode.

First, the processes up to the process illustrated in FIG. 2-7 in thefirst embodiment described above are performed. The n-type impuritydiffusion layer 3 is formed by diffusing phosphorus by thermal diffusionat a high temperature in phosphorus oxychloride (POCl₃) gas by using avapor-phase diffusion method such that the concentration of the n-typeimpurity element is uniform. Next, a silver paste 61 of the first layeris applied, by screen printing, to the anti-reflective film 4 on thelight receiving surface of the semiconductor substrate 11, andthereafter, the silver paste 61 of the first layer is dried. The printedpattern of the silver paste 61 of the first layer has a shapecorresponding to the shape of the surface silver grid electrodes 5 andthe surface silver bus electrodes 6 in a similar manner to the case ofthe first embodiment. FIG. 9-1 is a plan view illustrating a state wherethe silver paste 61 of the first layer is printed on one surface side ofthe semiconductor substrate 11. FIG. 9-2 is an enlarged viewillustrating the relevant parts in the region B, the region C, and theregion D in FIG. 9-1. In FIG. 9-2, (a) illustrates the region B, (b)illustrates the region C, and (c) illustrates the region D in anenlarged scale.

At this point in time, the silver paste 61 of the first layer is printedsuch that the printed pattern thereof and the printing method forprinting it are similar to those when the n-type doping paste 21 isprinted in the first embodiment described above. In other words, thecomb-tooth-shaped printed patterns get thinner as they get closer in theX direction in FIG. 9-1 to a comb-tooth-shaped printed pattern 61C(hereinafter, sometimes referred to as a central printed pattern 61C) ofthe silver paste of the first layer located in the center in the Xdirection. Therefore, the printing width of a comb-tooth-shaped printedpattern 61L (hereinafter, sometimes referred to as a left-end printedpattern 61L) of the silver paste of the first layer located at the leftend in the X direction in FIG. 9-1 and a comb-tooth-shaped printedpattern 61R (hereinafter, sometimes referred to as a right-end printedpattern 61R) of the silver paste of the first layer located at the rightend in the X direction are the largest. In other words, a width “h” ofthe left-end printed pattern 61L and the right-end printed pattern 61Ris the largest. A width “i” of the central printed pattern 61C is thesmallest. Then, after the silver paste 61 of the first layer is printed,the silver paste 61 of the first layer is dried.

In the printed pattern of the silver paste 61 of the first layer, asillustrated in FIG. 9-1 and FIG. 9-2, an alignment mark portion 62L isprinted with the silver paste 61 of the first layer in the region B inthe central portion in the extending direction of the left-end printedpattern 61L located at the left end in the X direction in FIG. 9-1. Thealignment mark portion 62L is printed with the silver paste 61 of thefirst layer in a specific shape, for example, projecting from theleft-end printed pattern 61L.

In the printed pattern of the silver paste 61 of the first layer, asillustrated in FIG. 9-1 and FIG. 9-2, an alignment mark portion 62R isprinted with the silver paste 61 of the first layer in the region D inthe central portion in the extending direction of the right-end printedpattern 61R located at the right end in the X direction in FIG. 9-1. Thealignment mark portion 62R is printed with the silver paste 61 of thefirst layer in a specific shape, for example, projecting from theright-end printed pattern 61R.

The alignment mark portion 62L and the alignment mark portion 62R areused for accurately superposing a silver paste 63 of the second layer onthe silver paste 61 of the first layer in the subsequent printingprocess of the silver paste 63 of the second layer.

Next, the silver paste 63 of the second layer is printed. FIG. 10-1 is aplan view illustrating a state where the silver paste 63 of the secondlayer is printed on one surface side of the semiconductor substrate 11.FIG. 10-2 is an enlarged view illustrating the relevant parts in theregion B, the region C, and the region D in FIG. 10-1. In FIG. 10-2, (a)illustrates the region B, (b) illustrates the region C, and (c)illustrates the region D in an enlarged scale. When the silver paste 63of the second layer is printed, an alignment mark portion 64L is printedwith the silver paste 63 of the second layer in the region B in thecentral portion in the extending direction of a comb-tooth-shapedprinted pattern 63L (hereinafter, sometimes referred to as a left-endprinted pattern 63L) of the silver paste of the second layer located atthe left end in the X direction in FIG. 10-1. The alignment mark portion64L has a specific shape, for example, projecting from the left-endprinted pattern 63L and has a shape corresponding to the alignment markportion 62L of the left-end printed pattern 61L.

When the silver paste 63 of the second layer is printed, an alignmentmark portion 64R is printed with the silver paste 63 of the second layerin the region D in the central portion in the extending direction of acomb-tooth-shaped printed pattern 63R (hereinafter, sometimes referredto as a right-end printed pattern 63R) of the silver paste of the secondlayer located at the right end in the X direction in FIG. 10-1. Thealignment mark portion 64R has a specific shape, for example, projectingfrom the right-end printed pattern 63R and has a shape corresponding tothe alignment mark portion 62R of the right-end printed pattern 61R.

The silver paste 63 of the second layer is printed such that the printedpattern thereof and the printing method for printing it are similar tothose when the silver paste 12 a is printed in the first embodimentdescribed above. In other words, the silver paste 63 of the second layeris printed such that the alignment mark of the silver paste 63 of thesecond layer matches the alignment mark of the silver paste 61 of thefirst layer. Specifically, the position (print position of the silverpaste 63 of the second layer) of the printing stage for printing thesilver paste 63 of the second layer is adjusted such that the positionof the alignment mark portion 62L matches the position of the alignmentmark portion 64L and the position of the alignment mark portion 62Rmatches the position of the alignment mark portion 64R. At this point intime, the positioning reference point, at which the silver paste 61 ofthe first layer and the silver paste 63 of the second layer aresuperposed on each other with the highest accuracy, is the centralportion within the surface of the semiconductor substrate 11. In FIG.10-1, the positioning reference point is indicated by a cross mark.

The printing mask used for printing the silver paste 63 of the secondlayer is a printing mask that has a plurality of opening patternsdisposed in parallel at equal intervals. The opening patterns have thesame width that is smaller than the width of the pattern of the silverpaste 61 of the first layer that is closest to the positioning referencepoint in the width direction of the surface silver grid electrodes 5.The pattern of the silver paste 61 of the first layer that is closest tothe positioning reference point in the width direction of the surfacesilver grid electrodes 5 and the opening pattern corresponding to theposition of the pattern of that silver paste 61 of the first layer arealigned with the highest accuracy.

The comb-tooth-shaped portions in the printed pattern of the silverpaste 63 of the second layer are also printed on the comb-shaped silverpaste 61 of the first layer in a similar manner. The pattern of thesilver paste 63 for forming the surface silver bus electrodes 6 is alsoprinted on the corresponding silver paste 61 of the first layer. Thesilver paste 63 of the second layer for the surface silver gridelectrodes is printed such that it has a uniform printing width “j”. Thesilver paste 63 of the second layer for the surface silver gridelectrodes 5 is printed such that the printing intervals in the silverpaste 63 are all the same.

The printed portion of the silver paste 61 of the first layer and theprint position of the silver paste 63 of the second layer are alignedwith reference to the positioning reference point (they are superposedwith high accuracy near the positioning reference point). Therefore,even when extension, distortion, or the like occurs in the printing maskused for printing the silver paste 63 of the second layer, printingmisalignment does not occur near the positioning reference point becausethe printing accuracy is high near the positioning reference point.

The print position of the silver paste 63 of the second layer isgradually displaced as it becomes further away from the positioningreference point; therefore, printing misalignment occurs. Thus, thesilver paste 61 of the first layer that is located away from thepositioning reference point has a certain width such that the silverpaste 63 of the second layer does not protrude from the silver paste 61of the first layer during the printing process of the silver paste 63 ofthe second layer. In other words, the comb-tooth-shaped portions in thepattern of the silver paste 61 of the first layer are such that thecomb-tooth-shaped patterns get thicker as they get further away from thepositioning reference point. Therefore, even when the printing mask forprinting the silver paste of the second layer has a printingmisalignment amount “k” because of its extension, distortion, or thelike, the silver paste 63 of the second layer is printed without theprinted portion of the silver paste 63 of the second layer protrudingfrom the printed portion of the silver paste 61 of the first layer.

Because the printing accuracy of the silver paste 63 of the second layeris high at a position near the positioning reference point, the width ofthe silver paste 61 of the first layer is made smaller near thepositioning reference point. Accordingly, the silver paste 63 of thesecond layer is printed without the printed portion of the silver paste63 of the second layer protruding from the printed portion of the silverpaste 61 of the first layer.

In such a manner, even the surface silver grid electrode 5 located awayfrom the positioning reference point in the width direction of thesurface silver grid electrodes 5 can be printed without causing printingmisalignment of the printed portion of the silver paste 63 of the secondlayer from the printed portion of the silver paste 61 of the firstlayer. Accordingly, the electrode area near the positioning referencepoint can be reduced. Thus, a reduction in the light receiving surfacearea due to the light-receiving-surface-side electrode is prevented andthus the photoelectric conversion efficiency of the solar cell can beimproved. Therefore, the properties of the solar cell can be improvedand the cost of forming the light-receiving-surface-side electrode canbe reduced.

Therefore, according to the second embodiment, a solar cell is obtainedin which a reduction in the photoelectric conversion efficiency due tothe printing misalignment of the light-receiving-surface-side electrodeis prevented and that has excellent photoelectric conversion efficiency.

In the above description, an explanation has been given of a case wherea multi-layer electrode is formed by printing an electrode paste aplurality of times in a superposed manner in a solar cell that does nothave a selective emitter structure; however, this case can be applied toelectrode formation of a solar cell that has a selective emitterstructure according to the first embodiment.

A solar cell module having excellent photoelectric conversion efficiencycan be obtained by forming a plurality of solar cells each having aconfiguration described in the above embodiments and electricallyconnecting the adjacent solar cells in series or in parallel. In such acase, for example, it is satisfactory if thelight-receiving-surface-side electrode 12 of one of the adjacent solarcells and the back-surface-side electrode 13 of the other of theadjacent solar cells are electrically connected.

INDUSTRIAL APPLICABILITY

As described above, the solar cell according to the present invention isuseful for obtaining a solar cell that prevents printing misalignment ofan electrode from occurring and has excellent photoelectric conversionefficiency.

REFERENCE SIGNS LIST

-   1 solar cell, 2 semiconductor substrate, 3 n-type impurity diffusion    layer, 3 a first n-type impurity diffusion layer, 3 aL    comb-tooth-shaped pattern (left-end first n-type impurity diffusion    layer) of first n-type impurity diffusion layer 3 a located at the    left end, 3 aR comb-tooth-shaped pattern (right-end first n-type    impurity diffusion layer) of first n-type impurity diffusion layer 3    a located at the right end, 3 aC comb-tooth-shaped pattern (central    first n-type impurity diffusion layer) of first n-type impurity    diffusion layer 3 a located in the center, 3 b second n-type    impurity diffusion layer, 3 aL3 comb-tooth-shaped first n-type    impurity diffusion layer located third from the left, 4    anti-reflective film, 5 surface silver grid electrode, 5 a silver    paste, 5 aC comb-tooth-shaped printed pattern (central printed    pattern) of surface silver grid electrode located in the center, 5    aL comb-tooth-shaped printed pattern (left-end printed pattern) of    surface silver grid electrode located at the left end, 5 aR    comb-tooth-shaped printed pattern (right-end printed pattern) of    surface silver grid electrode located at the right end, 6 surface    silver bus electrode, 7 back aluminum electrode, 7 a aluminum paste,    8 back silver electrode, 8 a silver paste, 11 semiconductor    substrate, light-receiving-surface-side electrode, 12 a silver    paste, 13 back-surface-side electrode, 21 n-type doping paste, 21C    comb-tooth-shaped printed pattern (central printed pattern) of    n-type doping paste located in the center, 21L comb-tooth-shaped    printed pattern (left-end printed pattern) of n-type doping paste    located at the left end, 21R comb-tooth-shaped printed pattern    (right-end printed pattern) of n-type doping paste located at the    right end, 22L, 22R alignment mark portion, 31 printing stage, 32    print substrate, 33 stationary camera, 34 image processing    apparatus, 35 reference image, 35L, 35R, 41L, 41R, 42La, 42Lb, 42L3,    51L, 51R alignment mark portion, 61 silver paste of first layer, 61L    comb-tooth-shaped printed pattern (left-end printed pattern) of    silver paste of first layer located at the left end, 61R    comb-tooth-shaped printed pattern (right-end printed pattern) of    silver paste of first layer located at the right end, 62L, 62R    alignment mark portion, 63 silver paste of second layer, 63L    comb-tooth-shaped printed pattern (left-end printed pattern) of    silver paste of second layer located at the left end, 63R    comb-tooth-shaped printed pattern (right-end printed pattern) of    silver paste of second layer located at the right end, 64L, 64R    alignment mark portion, a width of left-end printed pattern 21L and    right-end printed pattern 21R and width of left-end first n-type    impurity diffusion layer 3 aL and right-end first n-type impurity    diffusion layer 3 aR, b width of central printed pattern 21C and    width of central first n-type impurity diffusion layer 3 aC, c    printing width of silver paste for surface silver grid electrode, d    printing misalignment amount, e width of left-end first n-type    impurity diffusion layer 3 aL, f width of right-end first n-type    impurity diffusion layer 3 aR, g printing misalignment amount, h    width of left-end printed pattern 61L and right-end printed pattern    61R, i width of central printed pattern 61C, j printing width of    silver paste of second layer for surface silver grid electrode, k    printing misalignment amount.

1. A solar cell comprising: a first-conductivity-type semiconductor substrate that includes an impurity diffusion layer on one surface side, which is a light receiving surface side, the impurity diffusion layer having a second-conductivity-type impurity element diffused therein; a plurality of linear light-receiving-surface-side electrodes that are a paste electrode that has a multi-layered structure, is formed by multi-layer printing of an electrode material paste on the one surface side, and is electrically connected to the impurity diffusion layer and that extend in parallel in a specific direction in a plane direction of the semiconductor substrate; and a back-surface-side electrode that is formed on another surface side of the semiconductor substrate, wherein in the light-receiving-surface-side electrodes, the light-receiving-surface-side electrodes get smaller in width as the light-receiving-surface-side electrodes get closer in a width direction of the light-receiving-surface-side electrodes to a specific reference position.
 2. The solar cell according to claim 1, wherein the light-receiving-surface-side electrodes each include, in the multi-layered structure, a lower-layer portion and an upper-layer portion formed over the lower-layer portion, the lower-layer portions of the light-receiving-surface-side electrodes get smaller in width as the lower-layer portions get closer in the width direction of the light-receiving-surface-side electrodes to the specific reference position, and the upper-layer portions of the light-receiving-surface-side electrodes have a same width that is smaller than a width of the lower-layer portions formed in a region under the upper-layer portions.
 3. The solar cell according to claim 1, wherein the specific reference position is a position at which a positional accuracy in the width direction of the light-receiving-surface-side electrodes between the lower-layer portions and the upper-layer portions is highest.
 4. A manufacturing method of a solar cell comprising: a first step of forming an impurity diffusion layer on one surface side of a first-conductivity-type semiconductor substrate, which is to be a light receiving surface side, by diffusing a second-conductivity-type impurity element into the one surface side of the semiconductor substrate; a second step of forming a plurality of linear light-receiving-surface-side electrodes on the one surface side of the semiconductor substrate by multi-layer printing of an electrode material paste by using screen printing, the light-receiving-surface-side electrodes extending in parallel in a specific direction in a plane direction of the semiconductor substrate and being electrically connected to the impurity diffusion layers; and a third step of forming a back-surface-side electrode on another surface side of the semiconductor substrate, the back-surface-side electrode being electrically connected to the another surface side of the semiconductor substrate, wherein the second step includes printing a lower-layer electrode material paste during the multi-layer printing with a plurality of printed patterns that get smaller in width as the printed patterns get closer in a width direction of the light-receiving-surface-side electrodes to the specific reference position, and printing, by using a printing mask that has a plurality of opening patterns disposed in parallel at equal intervals in the width direction of the light-receiving-surface-side electrodes, an upper-layer electrode material paste during the multi-layer printing on the printed patterns of the lower-layer electrode material paste such that a printed pattern of the lower-layer electrode material paste that is closest to the specific reference position in the width direction of the light-receiving-surface-side electrodes and an opening pattern corresponding to a position of the printed pattern are aligned with each other, the opening patterns having a same width that is smaller than a width of the printed pattern of the lower-layer electrode material paste that is closest to the specific reference position in the width direction of the light-receiving-surface-side electrodes.
 5. The manufacturing method of a solar cell according to claim 4, wherein the second step includes printing, when the lower-layer electrode material paste is printed, first alignment mark portions for positioning at a plurality of predetermined locations in the printed patterns of the lower-layer electrode material paste, and printing, when the upper-layer electrode material paste is printed, the upper-layer electrode material paste such that second alignment mark portions for positioning are aligned with the first alignment mark portions at corresponding positions, the second alignment mark portions being provided at a plurality of predetermined locations corresponding to positions of the first alignment mark portions in a printed pattern of the upper-layer electrode material paste, and the specific reference position is a position at which a positional accuracy in the width direction of the light-receiving-surface-side electrodes between the printed patterns of the lower-layer electrode material paste and the opening patterns is highest when the first alignment mark portions and the second alignment mark portions are aligned with each other.
 6. A solar cell module comprising at least two solar cells according to claim 1 that are electrically connected in series or in parallel. 